Short answers, pulled from the story.
334 people died in the Beslan school siege, including 186 children. The city of Beslan counts 335 on its official website, reflecting a librarian named Yelena Avdonina who succumbed to her injuries on the 8th of December 2006.
Chechen warlord Shamil Basayev publicly claimed responsibility on the 17th of September 2004, stating the operation was carried out by his Riyad-us Saliheen brigade. Basayev said the attack cost 8,000 euros and that he had originally planned to target a school in Moscow or Saint Petersburg.
The cause remains contested. The official Torshin Report concluded the militants deliberately detonated their own bombs. Dissenting parliamentary investigator Yuri Savelyev concluded in a 280-page report that the first blast was caused by a Russian Shmel thermobaric rocket fired from the roof of a nearby building at No. 37 School Lane.
The Beslan school siege lasted three days, from the 1st to the 3rd of September 2004. The hostages in the gymnasium spent approximately 52 hours without food or water before the final assault began.
Following Beslan, Putin signed legislation replacing the direct election of regional governors with a presidential appointment system. He also oversaw changes to State Duma elections that eliminated single-mandate districts, and the Kremlin increased control over media and pressure on foreign-funded non-governmental organisations.
Nur-Pashi Kulayev was the only attacker captured alive at Beslan, found hiding under a truck. He was sentenced to life in prison on the 26th of May 2006, after which he disappeared into the Russian prison system. Russian officials confirmed in 2007 that he was alive, and he reportedly submitted a request for a case review in 2021.